Perhaps the most important unmet challenge in color science today is the provision and analysis of a new body of data on the perceptibility of moderate-size color differences. The objective of this research is to provide this analysis using Target Color's innovative method of microprocessor-driven sample production, accepted psychophysical methods of visual observations and scaling, and established methods of statistical analysis. The study is divided into three stages: 1, sample preparation; 2, collection of visual data; and 3, analysis to generate perceptibility ellipsoids. Running in part concurrently, these stages will require two years for completion. At up to 150 defined color centers covering the color gamut available, clusters of about 50 samples each will be prepared with accurate spacing at predetermined locations around a standard. Observers will be selected, tested for all pertinent aspects of color vision, and trained. Using established experimental conditions, they will perform psychophysical scaling experiments by the pair comparison method, among others. Likelihood analysis of the visual data will provide color-difference ellipsoids constituting a body of information relevant to normal color vision and to color tolerances for the manufacture and control of colored products.